Google officially launched its own wireless service today. Project Fi marks a partnership with Sprint and T-Mobile to provide users with the fastest available connection, whether it's from Wi-Fi or one of the partner 4G LTE networks. Phones on Project Fi will automatically to connect free wireless hotspots and switch back to Sprint or T-Mobile's networks (whichever's quicker) whenever Wi-Fi isn't available. 

Plans start at $20 a month and increase by $10 for every GB of data used in the U.S. or abroad. At the end of the billing cycle, Project Fi will issue refunds for any unused data. So if you pay $30 for 3GB of data and only use 1.4GB, you'll get back $16. 

Google says it'll encrypt connections for security. Phone numbers for Project Fi plans will exist in a cloud, meaning users can talk or text on "just about any" phone, device or laptop. 

For now Project Fi is available by invite only and only works on the Nexus 6, a phone Google developed with Motorola. You can request an invite here